1. Technical Field
The present invention relates to bearing units, and to electrically powered motors furnished with the bearing units.
2. Description of the Related Art
With numerous fan motors and drive motors for disk-drive and like applications being installed in electronic devices these days, lower-noise motor operation is being called for, in part because occasions in which such devices are employed in the home and in the office are increasing.
Fan motors that adopt sliding bearings are one answer to this call. In such motors, a rotary shaft serving as the rotor section is inserted into a sleeve, wherein the rotary shaft is rotatably supported via a lubricating oil. Inasmuch as the rotary shaft in this configuration is axially shiftable with respect to the sleeve, a number of techniques have been proposed to prevent the rotary-shaft-furnished rotary section from coming out of the sleeve.
One example of such a technique is to magnetically attract the fore-end portion of the rotary shaft with an attracting magnet via a thrust bearing. The attracting magnet is disposed underneath the rotary shaft and the sleeve, and is accommodated in a cuplike back yoke. In turn, the back yoke is mounted in a holder that retains the sleeve.
In the structure just described, however, the holder and the back yoke are constituted from separate parts; moreover, the back yoke is mounted on the holder. A consequence of this makeup is that the lubricating oil retained in the sleeve can pass the joint between the holder and the back yoke, and leak out to the motor exterior. Oil thus leaking out of the motor dramatically compromises its reliability and endurance.